1. Field of the Art
The present invention relates to a motor pump used to drain residual water the level of which is relatively low. More particularly, the present invention pertains to an internal motor pump which is arranged such that a motor pump body is surrounded with a pump outer casing to define a space therebetween and pumped water is discharged to the outside through the space to thereby cool the motor.
2. Prior Art
A so-called external motor pump has heretofore been known in which a submerged motor pump is installed under water in a cistern. In this motor pump, a discharge port of the motor pump is opened into the cistern, and water which is to be pumped is led from the outside of the cistern to a suction port of the pump through a suction conduit and pumped water is discharged to the outside from a discharge port provided at the upper portion of the cistern. There is another prior art which is arranged such that wheels are attached to the bottom of the above-described external motor pump so that it is mobile (portable); a flexible suction conduit having its open end defined as a suction port is employed so that the suction conduit can be inserted into any liquid source; and a self-priming function is imparted to the pump in order to prevent pumping failure due to air lock in the case where the water level of the liquid source is relatively low. An air lock would otherwise be caused by air sucked in from the open end of the suction conduit together with the liquid as the liquid source is nearly drained. Such a portable external motor pump is, for example, disclosed in Japanese Utility Model Publication No. 53111/81.
Since the above-described external motor pump is mobile and has a self-priming function, it is possible to drain a liquid source, for example, a puddle in a public works site, with substantially no residual water being left.
However, since the above-described known motor pump is formed as an external motor pump in which a submerged motor pump is installed under water in a relatively large-sized cistern, and heavy wheels are attached in order to support the cistern, the overall dimensions and weight of the apparatus are considerably increased. Accordingly, a disadvantageously large amount of priming is needed for a self-priming operation at the time of starting the pump.
It has also heretofore been the practice to employ an internal motor pump arranged such that a motor pump body is surrounded with a pump outer casing to define a space therebetween and pumped water is discharged to the outside through the space while cooling the motor. Such an internal motor pump is, for example, shown in U.S. Pat. No. 3945771. In this prior art, however, since the space between the pump outer casing and the motor pump body is utilized only as a pump discharge passage serving as a motor cooling water passage, it has no self-priming function and, therefore, cannot drain residual water the level of which is relatively low.
Therefore, the object of the present invention is to provide a portable motor pump which is so designed that it is possible to drain residual water the level of which is relatively low and having an overall size and weight that are reduced to make it easy to carry.